Eisenmenger's Syndrome

Definition
A process in which a left-to-right shunt in the heart causes increased flow through the pulmonary vasculature, causing pulmonary hypertension, which in turn, causes increased pressures in the right side of the heart and reversal of the shunt into a right-to-left shunt.

Etiology
A number of congenital heart defects can cause Eisenmenger's syndrome, including atrial septal defects, ventricular septal defects, patent ductus arteriosus, and more complex types of acyanotic heart disease.

Pathogenesis
The left side of the heart supplies blood to the whole body, and as a result has higher pressures than the right side, which supplies only deoxygenated blood to the lungs. If a large anatomic defect exists between the sides of the heart, blood will flow from the left side to the right side. This results in high blood flow and pressure travelling through the lungs. The increased pressure causes damage to delicate capillaries, which then are replaced with scar tissue. Scar tissue does not contribute to oxygen transfer, therefore decreasing the useful volume of the pulmonary vasculature. The scar tissue also provides less flexibility than normal lung tissue, causing further increases in blood pressure, and the heart must pump harder to continue supplying the lungs, leading to damage of more capillaries.

The reduction in oxygen transfer reduces oxygen saturation in the blood, leading to increased production of red blood cells in an attempt to bring the oxygen saturation up. The excess of red blood cells is called polycythemia. Desperate for enough circulating oxygen, the body begins to dump immature red cells into the blood stream. Immature red cells are not as efficient at carrying oxygen as mature red cells, and they are less flexible, less able to easily squeeze through tiny capillaries in the lungs, and so contribute to death of pulmonary capillary beds. The increase in red blood cells also causes hyperviscosity syndrome.

A person with Eisenmenger's Syndrome is paradoxically subject to the possibility of both uncontrolled bleeding due to damaged capillaries and high pressure, and random clots due to hyperviscosity and stasis of blood. The rough places in the heart lining at the site of the septal defects/shunts tend to gather platelets and keep them out of circulation, and may be the source of random clots.

Eventually, due to increased resistance, pulmonary pressures may increase sufficiently to cause a reversal of blood flow, so blood begins to travel from the right side of the heart to the left side, and the body is supplied with deoxygenated blood, leading to cyanosis and resultant organ damage.

Treatment
In early childhood, surgical intervention can repair the heart defect, preventing most of the pathogenesis of Eisenmenger's syndrome. If treatment has not taken place, heart-lung transplant is required to fully treat the syndrome. If this option is not available, treatment is mostly palliative, using anticoagulants, pulmonary vasodilators such as bosentan, antibiotic prophylaxis to prevent endocarditis, phlebotomy to treat polycythemia, and maintaining proper fluid balance. These measures can prolong lifespan and improve quality of life.